Study identifies area of brain that perceives music

Listening to music evokes an intangible emotional reaction, but the neural basis of this reaction is complicated. Pitch, melody, rhythm and other components of music are all processed by various areas of the brain, and how it all fits together has (so far) remained mysterious. Despite attempts to locate a 'music processor' in the brain, no one neural population -- an 'ensemble' of nervous system cells -- had been identified that could respond selectively to music as opposed to speech or other noises. Now, an MIT study claims to have found this specific neural population for the first time.

Researchers were able to identify the right neural populations using functional resonance imaging (fMRI). Six neural populations were identified from the data, including the music-selective population, and another set that respond to speech. In all, 10 human subjects were monitored listening to 165 natural sounds, including speech, music and everyday noises such as footsteps, car engines and a phone ringing. "The music result is notable because people had not been able to clearly see highly selective responses to music before,” said Sam Norman-Haignere, co-author of the study.

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fMRI has traditionally been an obstacle in the mapping of the auditory system. fMRI measures neural activity through blood flow, which has a coarse spatial resolution. It can, as a consequence, be difficult to pinpoint the exact location of specific neural events. To refine this, researchers used a technique that "models each voxel as a mixture of multiple underlying neural responses". "What we found is we could explain a lot of the response variation across tens of thousands of voxels with just six response patterns," Norman-Haignere said.

One population responded most to music, another to speech, and the other four to different acoustic properties such as pitch and frequency. The populations overlap with regions of the auditory cortex. "We think this provides evidence that there’s a hierarchy of processing where there are responses to relatively simple acoustic dimensions in this primary auditory area. That’s followed by a second stage of processing that represents more abstract properties of sound related to speech and music," Norman-Haignere said.

Researchers now hope to investigate whether or not the music-selective population contains subpopulations that respond accurately to a variety of aspects of music including, rhythm, melody and beat.